Bath and process for platinum and platinum alloys



United States Patent 7 ABSTRACT OF THE DISCLOSURE.

Directed to an electroless bath and method of depositing platinum and platinum alloys containing up to about 20% rhodium, up to about 10% iridium and up to about 10% ruthenium on an active surface wherein the bath is an alkaline platinum IV hydroxide solution containing about 2 to about grams per liter of platinum, an alkali metal hydroxide to give a minimum bath pH of about 8, up to about 1 mole per liter of a stabilized such as ethylamine, and up to about 1 gram per literof hydrazine. Platinum deposits produced in the absence of the stabilizer have catalytic properties whereas platinum and platinum alloy depositsproducedin the presence ofthe stabilizer are bright.

The present invention relates to the production of composite powders and, more particularly, to the production' of powder and powder compacts having a platinum deposit on the powder particle surface. It also relates to the deposition of protective coatings of platinum and platinum alloys on a number of less noble metals.

It is well known that one metal can be coated with a layer of another metal by various processes, including welding, vapor deposition, soldering, chemical deposition, electroplating and the like. Composite products produced thereby have utility in numerous applications which are commonly encountered. Thus, for example, platinum is commonly electrodeposited on various substrates for the purpose of providing'a corrosion resistant layer thereon. When it is required to provide a surface layer having practical utility as a catalyst, however,'the choice of methods of deposition isseverely limited. For example, if a process involving even moderate heat is used, the product is like ly to exhibit poor catalytic activity. Likewise, deposition processes involving the use of many chemical agents, e.g., sulfides or phosphides, can introducesmall but deleterious amounts of poisons into what mightotherwise be expected to be an actively catalytic deposit. For theseand manyother reasons, it is the fact that at present there is no industrially satisfactory method of producing catalytically active deposits of platinum on substrates such as nickel pow'der and graphite powder compacts. The continuing development of chemo-electric devices such as fuel cells has brought tofltheforeground the need for a commercially practical process for producing catalytically activev platinumdeposits on substrates such as powdered nickel and graphite. Although attempts were made to provide such. a commercially operative process, none, as far aswe are aware, wasentirely successful when carried into practice commercially on an industrial scale. 7

It has .now been discovered that by use of a novel process, particulate materials such as nickel powder and graphite powder compacts can be provided with an advantageous catalytically active platinum deposit.

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It is an object of the present invention to provide a novel process for the production of a catalytically active platinum deposit.

Another object-of the invention is to provide a novel process for the production of catalytically active platinumnickel and platinum-graphite structures.

The invention also contemplates providing catalytically active composite structures made by a novel process.

The invention is also directed to a process for the deposition of platinum and of several platinum alloys which are useful as decorative surfaces or as protective coatings for less noble metals.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates a non-electrolytic process for depositing platinum and platinum alloys containing a metal from the group consisting of rhodium, iridium and ruthenium on surfaces, including nickel, copper and graphite surfaces, comprising chemically reducing the said platinum metals from a complex alkaline platinum IV hydroxide solution upon an active substrate material by the action of hydrazine. The reduction process as contemplated in accordance with the present invention is an autocatalytic reaction, that is, deposited platinum metal or alloy itself catalyzes additional deposition of the platinum metal or alloy.

Broadly stated, aqueous solutions or baths from which platinum can be deposited contain, in solution as the platinum IV hydroxide, about 2 to 20 grams per liter (g.p.l.), e.g., about 2.4 to about 10 g.p.l., of platinum, about 0.1 to about 1 g.p.l. of hydrazine, an amount of a soluble alkali metal hydroxide suflicient to give a minimum pH of about 8, e.g., pH 9 or pH 10 or higher, and up to about 1 'mole per liter (-m.p.l.), e.g., about 0.01 to about 1 rn.p.l., of a bath-soluble and bath-compatible stabilizer characterized by a trivalent nitrogen integer and exemplified by compounds from the group consisting of ethylamine, the sodium salt of ethylene diamine tetraacetic acid (EDTA), quinoline and sulfamate ion (added to the bath, for example, as sulfamic acid). Materials such as nickel and alloys thereof, graphite, iron, copper, molybdenum, silver, tantalum, and titanium can be coated with platinum merely by immersing them in the aforedescribed solutions and holding them therein while-maintaining the temperature of .the solution, at about 25. C. to about 35 C. Bath compositions contemplated in accordance with the invention are stable and can be stored. Generally, hydrazineis not added to the bath until plating is to bestarted.

The "bath may readily be prepared by boiling a water solution of chloroplatinic acid with anexcess vof sodium hydroxide. The end point of the reaction is marked by a solution color change from the characteristic blood red of chloroplating acid to an orange characteristic of a water solution containing sodium platinum IV hydroxide [Na Pt(OH) Sodium chloride generated by the reaction is not harmful. The bath pH is maintained well over on the alkaline side, e.g., pH 8 or higher, to prevent undesired hydrolysis of the solution.

When it is desired to produce platinum alloy deposits with metals from the group consisting of rhodium,,-iridium, and ruthenium, bath-soluble salts of these metals are introduced into the bath. Suitable salts for this purpose include ammonium rhodium III chloride and the corresponding salts of iridium and ruthenium, rhodium III nitrate [Rh(NO diammonium sodium rhodium III chloride [(NH NaRhCl and ammonium rhodium III nitrite [(NH Rh(NO Rhodium can be introduced into the bath in amounts up to about 20%, by weight of the platinum content of the bath while iridium and ruthenium can be introduced into the ba h in amounts up to about 10%, by weight, of the platinum content of the bath. Hydrazine may be added to the bath as the hydrate solution or as hydrazine sulfate or hydrazine chloride dissolved in water or in solution with sodium or potassium hydroxide.

In accordance with the present invention, it is contemplated to deposit platinum or platinum alloys upon the surface of nickel and carbon (graphite) particles and within the pores of porous nickel and graphite structures: Such deposits are of a finely divided nature, have an extended surface, have enhanced catalytic properties, and are useful in the production of fuel cell electrodes and other catalytic bodies. These finely divided catalytic deposits are advantageously produced from baths deV id of any stabilizer. An advantageous bath composition for providing catalytic deposits is set forth in Table I:

Table I Pt (as sodium platinum IV hydroxide) 5.2 to 7.2 g.p.l. NaOH to pH 12.5. Hydrazine 0.5 to 1 g.p.l. Water Balance.

A bath such as set forth in Table I can be used at a temperature of about 25 C. to about 30 C. When f rmulating such a bath it is necessary to avoid contaminants which may tend to inhibit the catalytic properties of the deposited platinum. Thus, elements such as lead, arsenic, and dimethylglyoximine should be carefully excluded from the bath. It is also contemplated in accordance with invention to employ baths wherein the hydrazine content at any given moment is low, e.g., about 0.1 g.p.l. to about 0.2 g.p.l. Hydrazine preferably can be added either continuously or in portions during a deposition run.

When a bright metallic appearing deposit of platinum is to be produced on a metal surface, a stabilizer such as ethylamine is also employed in the bath and a bath composition as set forth in Table II is quite suitable.

Table II Pt (as sodium platinum IV hydroxide) about 10 g.p.l. NaOH to pH 10. Hydrazine 0.1 to 1 g.p.l. Ethylamine 0.5 to 45 g.p.l. Water Balance.

Baths such as set forth in Table II can be used at temperatures of about 25 C. to about 35 C. and should be devoid of those aforelisted substances which interfere with deposition of the platinum.

For the purpose of giving those skilled in the art a better understanding of the invention and/or a better appreciation of the advantages of the invention, the following illustrative examples are given:

EXAMPLE I An aqueous bath containing about 5.2 g.p.l. of sodium platinum IV hydroxide (approximately 3 g.p.l. platinum) and about 10 g.p.l. of NaOH was prepared and a quantity of very finely divided carbonyl nickel powder was stirred into the bath. The bath was warmed to 30 C. and about 1 g.p.l. of hydrazine was added. After a time, the bath was found to be devoid of platinum which was deposited in finely divided form on the nickel powder. After washing and drying the metal powder, it was not possible to separate the platinum from the nickel by magnetic or flotation methods.

EXAMPLE 11 Nickel powder was successfully coated with a catalytically active platinum deposit by barrel plating said nickel powder using a barrel made of a clear polymethylmethacrylate plastic material and a bath similar to the bath employed in Example I except that hydrazine was added in small increments during the run. Plating time was 150 minutes and the platinum content of the coated powder was about 5% by weight.

EXAMPLE III Graphite powder was successfully coated with platinum substantially as described in Examples I and II.

EXAMPLE IV A water solution containing about 5 g.p.l. of platinum as sodium platinum IV hydroxide with sodium hydroxide to give a solution pH of about 8 was prepared. Porous graphite discs about 0.25 inch thick and about 2.5 inches in diameter, having a total porosity of about 0.33 cubic centimeter per gram with approximately 85% of the pores having a pore diameter of about 0.8 to 10 microns and a weight of about 13 grams were soaked in a hydrazine solution having a one molar hydrazine concentration for about 15 minutes. The sodium platinum IV hydroxide solution was passed through the graphite discs in calculated quantity until the platinum content of the solution was exhausted. The discs were washed with distilled water until free of alkali, dried with alcohol and acetone and oven dried at 120 C. The discs were found to contain about 6% platinum by weight. The thus-prepared discs are satisfactory when employed as anodes in a methanol-oxygen fuel cell.

EXAMPLE V An aqueous bath containing 10 g.p.l. of platinum as sodium platinum IV hydroxide, about 5 g.p.l. of NaOH and about 10 g.p.l. of ethylamine was prepared. Two separate runs were made depositing platinum upon copper from this bath, one at 25 C. and the other at 35 C. Hydrazine was added in small increments to the bath to provide a concentration of about 1 g.p.l. therein. Bright, uniform, metallic appearing deposits of platinum were formed on copper under these conditions. Plating rate was about 300 microinches per hour at 25 C. and about 500 microinches per hour at 35 C.

Bright, uniform, metallic appearing deposits of platinum were formed on iron, molybdenum, nickel, silver and titanium under conditions similar to those employed in Example V.

Deposits of platinum-rhodium alloys may be produced on metallic surfaces according to the compositions set forth in Table III.

Table III Pt (as sodium platinum IV hydroxide) 10 to 20 g.p.l. Rh [as (NH RbCl 1 to 2 g.p.l. NaOH to pH 10. Hydrazine 2 to 45 g.p.l. Ethylamine 0.5 to 1 g.p.l. Water Balance.

Baths as set forth in Table III may be operated in the temperature range of from 25 C. to 35 C.

EXAMPLE VI active metal surfaces. It is also particularly advantageous in the production of platinum plates on surfaces such as printed circuits elements which cannot conveniently be coated by electrodeposition.

Alloys containing ratios up to 80 platinum to 20 rhodium using baths containing rhodium in amounts up to about 20% of the platinum content on a weight basis can be produced. Other alloys of platinum such as platinumiridium alloys containing up to about iridium, e.g., up'to about 5% iridium, and platinum-ruthenium alloys containing up to about 10% ruthenium, e.g., up to about 5% ruthenium, can be produced. As long as a stabilizer, e.g., ethylamine; is present in the bath, alloys are produced to substantially constant compositions in about the weight ratio of metals present in the bath.

Palladium cannot be plated from baths containing a strong alkali such as sodium hydroxide or potassium hydroxide because palladium precipitates from the baths. Accordingly, palladium may not be present in the bath in any appreciable amount and, most advantageously, is absent. While either sodium hydroxide or potassium hydroxide may be employed in preparing the bath, sodium carbonate and potassium carbonate may not be employed for the purpose because the carbonates cause slud-ging of the bath. Furthermore, ammonium hydroxide may not be employed in amounts exceeding about 1 g.p.l. calculated as ammonia (NH because greater amounts of ammonia cause precipitation of platinum from solution and also creates difficulties in plating upon a copper substrate.

The special bath provided in accordance with the invention may be considered, particularly with reference to platinum, as a solution in aqueous sodium (or potassium) hydroxide of a platinum salt. Sodium and/or potassium hydroxide may be present in the bath in amounts up to saturation.

As noted hereinbefore, the stabilizer, e.g., ethylamine, is characterized by a trivalent nitrogen integer and is bath-soluble and bath-compatible. Thus, those skilled in the art will recognize that immiscible, oily, tarry and otherwise physically undesirable compounds are not to be employed in the bath as otherwise the results achieved in accordance with the invention are not achieved.

It has been pointed out hereinbefore that platinum and platinum alloy deposits can be produced upon any clean active metal, alloy or carbon surface. Surfaces of materials such as glass, plastics and ceramics which are not active can be rendered active by depositing an active preliminary coat of a material such as platinum, palladium, etc. Surfaces made of copper, nickel, nickel alloys, iron, titanium, tantalum, carbon, molybdenum, etc., can be plated with platinum and platinum alloy deposits in accordance with the invention.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.

We claim:

1. A bath for depositing platinum consisting essentially of water, about 2 to about grams per liter of platinum as a platinum IX hydroxide, an alkali from the group consisting of sodium hydroxide and potassium hydroxide to provide a minimum bath pH of about 8, up to about 1 gram per liter of hydrazone, and up to about 1 mole per liter of a bath-soluble and bath-compatible stabilizer containing a trivalent nitrogen integer.

2. A bath for depositing a metal from the group consisting of platinum and platinum alloys with rhodium, iridium and ruthenium consisting essentially of water, about 2 to about 20 grams per liter of platinum as a platinum IV hydroxide, a metal from the group consisting of rhodium, iridium and ruthenium as a bath-soluble salt in an amount such that rhodium is up to about 20% by weight of platinum present and iridium and ruthenium are in amounts up to about 10% each by weight of platinum present, an alkali from the group consisting of sodium hydroxide and potassium hydroxide to provide a minimum bath of about 8, about 0.1 to about 1 gram per liter of hydrazine, and about 0.01 to about 1 mole per liter of a bath-soluble and bath-compatible stabilizer containing a trivalent nitrogen integer.

3. A bath according to claim 2 wherein the platinum content is about 10 to 20 grams per liter.

4. A bath for depositing platinum consisting essentially of water, about 2.4 to about 10 grams per liter of platinum as a platinum IV hydroxide, an alkali from the group consisting of sodium hydroxideand potassium hydroxide to provide a minimum bath pH of about 10, up to about 1 gram per liter of hydrazine, and up to about 1 mole per liter of a bath-soluble and bath-compatible stabilizer containing a trivalent nitrogen integer.

5. A bath according to claim 4 wherein the stabilizer is selected from the group consisting of ethylamine, the sodium salt of EDTA, quinoline and sulfamate ion.

6. A bath for depositing platinum consisting essentially of water, about 5.2 to about 7.2 grams per liter of platinum as sodium platinum IV hydroxide, an amount of sodium hydroxide to provide a bath pH of about 12.5, up to about 1 mole per liter of a bath-soluble and bathcompatible stabilizer containing a trivalent nitrogen integer, and hydrazine in an amount up to about 1 gram per liter.

7. A process for depositing platinum in a form comprising an extended surface and having enhanced catalytic properties which comprises immersing an active surface into a bath containing about 2 to about 20 grams per liter of platinum as a platinum IV hydroxide, an alkali from group consisting of sodium hydroxide and potassium hydroxide to provide a bath pH of at least about 8, and the balance essentially water, and introducing into said bath hydrazine in an amount up to about 1 gram per liter to deposit platinum upon said. active surface.

8. A process for depositing platinum which comprises immersing an active surface into a bath containing about 2 to about 20 grams per liter of platinum as a platinum IV hydroxide, an alkali from the group consisting of sodium hydroxide and potassium hydroxide to provide a bath pH of at least about 8, up to about 1 mole per liter of a bath-soluble and bath-compatible stabilizer containing a trivalent nitrogen integer, and the balance essentially water, and introducing into said bathhydrazine in an amount up to about 1 gram per liter to deposit platinum upon said active surface.

9. A process according to claim 8 wherein the active surface is made of a material from the group consisting of copper, nickel, nickel alloys, iron, titanium, tantalum, carbon, and molybdenum.

10. The process for depositing platinum and platinum alloys with rhodium, iridium and ruthenium which comprises establishing a bath containing about 2 to about 20 grams per liter of platinum as a platinum IV hydroxide, a metal from the group consisting of rhodium, iridium and ruthenium as a bath-soluble salt in an amount such that rhodium is up to about 20% by weight of platinum present and iridium and ruthenium are in amounts up to about 10% each by weight of platinum present, an alkali from the group consisting of potassium hydroxide and sodium hydroxide to provide a minimum bath pH of about 8, about 0.01 to about 1 mole per liter of a bathsoluble and bath-compatible stabilizer containing a trivalent nitrogen integer, and the balance essentially water, introducing into said bath hydrazine in an amount up to about 1 gram per liter, and introducing an active surface into said bath to deposit a metal from the group consisting of platinum and platinum alloys with rhodium, iridium and ruthenium thereon.

11. A process according to claim 10 wherein the platinum content in the bath is about 10 to about 20 grams per liter.

12. A process according to claim 11 wherein the bath pH is at least about 10.

13. A process for depositing platinum which comprises establishing a bath containing about 2.4 to about 10 grams per liter of platinum as sodium platinum IV hydroxide to provide a bath pH of about 10, up to about 1 mole per liter of a bath soluble and bath-compatible stabilizer containing a trivalent nitrogen integer, introducing into said bath hydrazine in an amount up to about 1 gram per liter, introducing into said bath an active surface, and depositing platinum upon said surface.

14. A process for depositing platinum which comprises establishing a bath containing about 5.2 to about 7.2 grams per liter of platinum as sodium platinum IV hydroxide, an amount of sodium hydroxide to provide a bath pH of about 12.5, up to about 1 mole per liter of a bath-soluble and bath-compatible stabilizer containing References Cited UNITED STATES PATENTS 2,872,359 2/1959 Saubestre 117l30 X 3,105,772 10/1963 Loiseleur 117--54 X 3,147,154 9/1964 Cole et a1 117130 X ALFRED L. LEAVITT, Primary Examiner T. E. BOKAN, Assistant Examiner US. Cl. X.R.

5333 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,485,923 Dated Dec. 30, 1969 Inventor-(s) Richard N. Rhoda and Ra m n It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, lines 58 and 59, in Table IIl, revise the order of numbers to read "Hydrazine 0.5 to l g.p.l1' and"Ethylamine 2 to 45 g.p.l.

Col. 5, line 6]., (line 3 of claim 1) change "IX" to -IV--. Same column, same claim, line 64, correct the spelling of "hydrazine".

Col. 6, line 4, (line 12 of claim 2) after "bath" add -pH--.

cc]. 7, line 6, (line 4 of claim 13) after "hydroxide" add --,an amount of sodium hydroxide-.

Signed and sealed this 29th day of June 1971.

(SEAL) Attest:

WARD M.FLETCHER JR. WILLIAM E. SCHUYLER, JR. fitesting Officer Commissioner of Patents 

